AGN Unification-1

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AGN Unification-1

• History
• The present status

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Aims and objectives

• Review the arguments that led to unified schemes.
• Outline the different schemes, their strengths
  and weaknesses.
• Suggest future lines of attack

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Whats all this Unification?

• Historically it is attempt to explain as much as
  the spread of observational properties as
  possible in terms of orientation effects.
• Assume some axis i.e. rotation
• More generally, it is an attempt to explain the
  diversity of observational properties in terms of
  a simple model

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The AGN Paradigm

• Annotated by M. Voit

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Introduction

• AGN are not spherically symmetric and thus what
  you see depends on from where you view them. This
  is the basis of most unification models.
• It was the discovery of superluminal motion and
  the interpretation in terms of bulk relativistic
  motion of the emitter that first made people
  realize that orientation in AGN was important.
• I will outline the consequences of Doppler
  boosting, describe the historical development of
  schemes and then review the modern evidence.
• N.B. Relativistic beaming is not the only
  mechanism that can make AGN emission anisotropic

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Doppler boosting

• When an emitting body is moving relativistically
  the radiation received by an observer is a very
  strong function of the angle between the line of
  sight and the direction of motion.
• The Doppler effect changes the energy and
  frequency of arrival of the photons.
• Relativistic aberration changes the angular
  distribution of the radiation.
• Is the Doppler factor
• Is the spectral index

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Practical consequences of boosting

• Superluminal motion implies Lorentz factors of 5
  to 10 gt possible boosting of flux density by
  1000.
• Sources with the strongest cores will be those
  viewed with their axes at small angles to the
  l.o.s.
• The highly boosted sources will only be a small
  percentage of the total population.
• But may be a large fraction of a flux limited
  sample

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Parent populations

• To every beamed source there will be many
  unbeamed sources the parent population.
• How to identify the parent population?
• Look at some emission thats isotropic e.g.
  radio lobe emission, far infrared emission,
  narrow-line emission, etc in the beamed
  population and look for another population having
  the same luminosity function for the isotropic
  emission.

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History of Unification

• Rowan-Robinson (1976, ApJ, 213,635) tried to
  unify Seyfert galaxies and radio sources.
• Mostly wrong no beaming
• But the importance of dust and IR emission
  correct.
• Blandford and Rees (Pittsburgh BL Lac meeting
  1978) laid the foundations for beaming
  unification. (Radio loud only).

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History continued

• Scheuer and Readhead (1979, Nature,277,182)
  proposed that radio core-dominated quasars and
  radio quiet quasars could be unified the former
  being beamed versions of the latter.
• Orr and Browne (1982,MNRAS,200,1067 ) realized
  the the Scheuer and Readhead scheme could not
  work because MERLIN and VLA had shown that most
  of the core-dominated quasars had extended
  (isotropic) radio emission and thus their parent
  population could not be radio quiet. We looked
  for a non-radio quiet parent population
• Proposed core-dominated/lobe-dominated
  unification for quasars

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Radio Galaxy/Quasar Unification(Both are FR2s)

• Widely discussed before, but first published by
  Barthel (1989, ApJ, 336,606) an extension of
  core-dominated/lobe-dominated quasar unification.
• Quasars have strong continuum and broad lines and
  radio galaxies (FR2s) have little continuum
  (other than starlight) and no broad lines.
• How could they be the same thing? Only if one
  could hide the quasar nucleus with something
  optically thick (a molecular torus).
• N.B. In a parallel line of development Antonucci
  and Miller had discovered polarized broad lines
  in the Seyfert 2 NGC1068 which they interpreted
  as being scattered nuclear radiation from a
  hidden BLR.

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The AGN Paradigm

• Annotated by M. Voit

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BL Lacs and FR1 RGs

• Similar arguments apply to these intrinsically
  lower luminosity objects BL Lacs are the beamed
  cores of FR1 RGs. (Note FR1 RGs generally have
  only weak and narrow emission lines and BLLacs
  are almost lineless.)
• Blandford and Rees (1978)
• Browne (1983, MNRAS,204,23)
• Antonucci and Ulvestad (1985,ApJ,294,158)
• Padovani and Urry (1991, ApJ,368,373)

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Evidence for BL Lac/FR1 unification

• The statistics look ok (Browne Padovani and
  Urry) for reasonable Lorentz factors
• The required relativistic jets are seen in a few
  FR1s, most notably in M87 (Biretta AJ,520,621).
• The strength of optical cores in FR1s seems to
  correlate with the strength of the radio core
  consistent with both being beamed (Capetti
  Celotti,1999,MNRAS,303,434, Chiaberge et al.
  2000,AA,358,104)
• gt No hidden BLR in FR1s (but BL Lac has a broad
  line)

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HST Image of jet in M87

• M87 is and FR1 radio galaxy
• Superluminal motion has been detected in both
  radio and optical

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Evidence for superluminal motion in M87
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NGC6251

• HST image of the optical core.
• Despite dust lane (dark band) the core is clearly
  visible
• The strength of cores correlated with that of
  radio core

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Correlation between optical nuclear and radio
core luminosities (Chiaberge et al,AA,358,104)
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Unification across the FR1/FR2 boundary?

• There does seem to be a real distiction between
  FR1s and FR2s
• Radio structure
• Radio luminosity
• Optical emission line properties (but remember BL
  Lac)
• Cosmological evolution
• But the non-thermal emission is similar in both
• Also FR2s could possibly evolve into FR1s
• There is no strong evidence against this
  (Unification by time?)

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FR2s evolving into FR1s?

• Assume
• FR2s are objects with relativistic jets that
  reach the full extent of the radio source
• That the distance that jets can travel at
  relativistic speeds depends on jet power high
  power jets make it further out.
• Then young small sources of a given jet power
  will be FR2s, but as they grow and get older they
  will become FR1s
• Some crossing of the FR boundary with time for
  lower-power objects.
• (N.B. There are some FR2s with weak emission
  lines which when beamed may become BL Lacs)

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Tests of radio galaxy/quasar unification

• The relative numbers of FR2 RGs and Qs (about
  21 gt half-cone angle of 45 degrees) should be
  related to the size of the un-obscured cone angle
  hence can calculate by what factor the radio
  sizes of Qs should be smaller than RGs.
• The results are mixed but do not rule anything
  out.
• If the quasar nucleus is hidden by dust the
  intercepted energy should be re-radiated in the
  FIR. Qs and RGs should have same FIR luminosity.
• Seems just about ok

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Tests continued

• Broad lines should be detectable in narrow line
  RGs either in scattered polarized light or in
  the IR.
• Some examples of both are seen as well as some UV
  broad lines (e.g. Cygnus A)
• Narrow emission lines well away from the torus
  should have the same luminosity in RGs and Qs of
  intrinsically the same power.
• OIII is stronger in Qs (Jackson and Browne)
• OII is the same (Hes et al.)
• The Q luminosity function should be a beamed
  version of the RG one (Urry and Padovani)
• This works

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Orientation indicators in radio-loud objects

• The ratio of an isotropic emission to a beamed
  emission should be an indicator of orientation.
• R Radio core/radio extended
• (Hine and Longair Orr and Browne)
• R5000 Radio core/5000 Angstrom continuum
• (Wills Brotherton, 1995,ApJ,448,81 )
• Can we use these to deduce something about the
  inner regions of AGN?

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Correlations Emission lines

• (Wills Baker Corbin Barthel Brotherton,
  Jackson, Browne and others have had fun in this
  area)
• The goal is to use correlation to test models
  and, more important, to learn about the inner
  regions of radio galaxies and quasars.
• What has been learnt?
• H-beta FWHM anti-correlates with R gt disk-like
  BLR (Wills and Browne). (Also some broadlines
  have disk-like profiles)
• OII and OIII equivalent widths suggests
  extinction even in the inner NLR (Baker, Barthel,
  Jackson Browne)
• Even the thermal (disk) continuum is orientation
  dependent in quasars.
• I cannot make sense of the wealth of information!

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Correlations -- Radio

• If jets are relativistic, some unification is
  inevitable. Whats the evidence for relativistic
  jets?
• Superluminal motion (rarely measurable in RGs)
• Jet asymmetry (X-ray jets seen with Chandra need
  relativistic motion to give enough IC emission)
• Laing Garrington effect
• Even in radio galaxies, the side of the source
  with the jet is less depolarized
• gt Jet asymmetry arises from orientation and
  hence they are relativistic.

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Radio map of 3C175
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CHANDRA X-Ray Jet in Pictor-A
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Wider Unification

• Stimulated by the discovery of polarized broad
  lines in a Seyfert 2 (narrow-line Seyfert) by
  Antonucci and Miller (1985,ApJ,297,621), in the
  mid 1980s the optical community realized that AGN
  were not spherically symmetric and that
  orientation effects were important.
• There emerged the standard model the key
  ingredient of which is the obscuring torus
  which hides the inner part of all AGN (BLR plus
  disk emission), both radio-quiet and radio-loud

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The Structure of AGN
Seyfert 1
Narrow Line Region
Torus
Central Engine Accretion DiskBlack Hole
Seyfert 2
Broad Line Region
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Evidence for the standard model

• More hidden BLR seen in scattered (polarized)
  light.
• Ionization cones.
• Though many claimed not many are convincing
• Photoionization considerations some Seyfert 2s
  do not have enough ionization photons seen to
  give the NLR luminosity
• Molecular disks, particularly NGC4258

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Ionization cone in NGC 5728

• If ionizing photons are blocked by the torus then
  one expects to see cones delineating the
  boundary.

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Conclusions about RG/Q unification

• Some radio FR2 galaxies have hidden Qs
• The simplest picture where there is a single
  un-obscured cone angle for all objects needs
  elaboration.
• Perhaps the Andy Lawrence (MN, 252,586) and Heino
  Falcke idea of a cone angle that depends on
  intrinsic luminosity (receding torus) is one of
  the most promising.
• Unified schemes seem to have run out of
  predictive power!